The photochemistry of the antitumor drugs adriamycin, daunomycin, certain quinolinium salts, and gilvocarcin V was investigated in relation to the possible combination of chemotherapy with photodynamic therapy. By the use of electron spin resonance and spin trapping techniques, and of (17-0) enriched water and oxygen, the relative contributions of superoxide radicals, hydroxyl radicals, and singlet oxygen to the photochemistry of these antitumor drugs was elucidated. The chemical effects of ultrasound were studied in relation to hyperthermia (used in combination with radiation therapy) and the possible consequences of diagnostic and therapeutic applications. The effect of varying the temperature of cavitation bubbles in the presence of different rare gases on free radical formation and the shearing stress induced by ultrasound on mammalian cells was measured. The hydroxyl radical yields were in the order xenon>kryton>argon>neon>helium in accord with the higher temperatures of the cavitation bubbles. However, mammalian cell lysis induced by shearing stress was the same for all rare gases and independent of their thermal conductivity and the temperature of the cavitation bubbles. The radicals generated in aqueous solutions of nucleic acid and protein components by ultrasound have been identified by spin trapping and compared with those formed by ionizing radiation and by UV-photolysis in the presence of hydrogen peroxide. The observed isotopic exchange reactions suggest the possible use of sonochemical methods for the synthesis of deuterated protein and nucleic acid constituents.